Re: [Erlyaws-list] Accept-Encoding & deflate

[Steve V. <vi...@ie...>]

On Fri, Jan 17, 2014 at 4:44 AM, Nicolas Thauvin <ni...@co...>wrote:

> Hi !
>
>   While trying to play with Google PageSpeed Insights, our website was
> reported as "not using compression for JS & CSS files" whereas the
> "deflate" option was correctly set in the config file.
>
> Actually, this Google bot sends two headers "Accept-Encoding:gzip,deflate"
> when requesting those files, which results in a weirdness inside yaws.erl :
>
> accepts_gzip(H, Mime) ->
>      case [Val || {_,_,'Accept-Encoding',_,Val}<- H#headers.other] of
>          [] ->
>              false;
>          [AcceptEncoding] ->
>            [...];
>          _ -> false
>      end.
>
> The third branch wins, and gzip is disabled. I patched the second match as
> [AcceptEncoding | _] to pass Insights tests, but I wonder what behavior is
> expected according to the RFCs :
>   * concatenate the list of all encodings in all headers ?
>   * take the first header ?
>   * ... ?
>

According to HTTP 1.1 section 4.2, a receiver may combine multiple
instances of any header whose value can be a comma-separated list, which
applies in this case. Looks like HTTPbis in section 3.2.2 keeps the same
rule. So, technically Yaws should be combining the multiple Accept-Encoding
headers into one here. I'll make that change.

It looks like a bug on Google side (I wrote a comment in the Insights
> tool), but Yaws' reply seems weird to me !
>

I think the Google side is OK in this case.

--steve